Modulation



April 30, 1935. j w. BUscHBEcK 1,999,892

MODULATION Filled Feb. 18, 1935 i391 Jay-g2 INVENTOR iff/wfg ,susa/afm ATTORNEY Patented Apr. 30, 1935 UNITED STATES PATENT. oFFICE MODULATION Werner Buschbeck, Berlin, Germany,` assigner to Telefunken Gesellschaft fr Drahtlose Telegraphie m. b. H., Berlin, Germany, a corporation of Germany Application February 18, 1933, Serial No. 657,377 In Germany March 11, 1932 3 Claims.

linear modulation curves in modulation methods Y based upon grid action may be minimized as much as possible, it is known from the prior art that auxiliary direct current may be added to the grid direct current; and if the former be chosen sufficiently large is able to reducethe non-linear influences of the grid direct current to any desired degree.

In describing the invention reference will be made to the drawing in Which Figure 1 shows a circuit arranged in accordance with the present invention, while Figures 2, 3 and 4 show modifications of the arrangement of Figure 1.

In Figure l, H is the main transmitter valve, M the modulator tube, Ez the source for the additional direct current which ilows by way of resistance Rz between the anode and cathode of M, V a grid biasing battery to maintain the grid of the modulator tube at the desired negative potential. It will be understood that a large additional direct current requires a larger number of modulator tubes as well as a supplemental electromotive force of greater value.

Now, according to the present invention the identical result is to be obtained with essentially smaller expenditures in that the grid biasing potential of the modulator tubes is derived from the fall of potential caused by the supplemental direct current IZ between the anode and cathode of M, across the resistance Rz (Figure 2) rather than being supplied, according to prior practice, from a xed electromotive force. Several voltages are active across the terminals of resistance RZ. The potential drop in Rz due to the current caused by the additional electromotive force EZ to flow in the anode to cathode circuit of M is added to the voltage ER set up across the impedance of the modulator tube M by the current Ig, which flows between the cathode and grid of tube H due to grid rectication. These voltage drops are in parallel between the control grid and cathode of tube H as clearly shown. The algebraic sum of these voltages is applied between the control grid and cathode of tube H to determine the grid bias thereof. Now, if the grid direct current due to grid rectiiication rises more markedly than linearly, then the voltage ER across the modulator tube impedance increases more strongly than linearly also. This voltage opposes the supplemental voltage Ez and causes the supplemental direct current to fall oif faster than linearly and thus also causes the voltage across the modulator tube to decrease -faster than linearly, the resistance of the latter decreasing more rapidly than linearly with the consequence that the effect of non-linear current due to grid rectification is counteracted. At the same time, by the arrangement to be chosen according to the invention, adistinct grid biasing electromotive force for the modulator tube may be dispensed with.

Inorder that the size of the compensating actions may be rendered independent of the grid biasing voltage, it will be feasible to provide in series with the grid tap a distinct electromotive force B (Figure 3) which for modulation purposes, i. e., for dynamic actions may be replaced Valso by a double tap BI, B2 (Figure 4) by way with a work circuit, and a circuit for modulating the carrier waves from said source lin said relay, f

said circuit including means for insuring said modulation of said carrier is linear with respect to the modulating potentials comprising, a modulator tube having anode, cathode and control grid, a connection between the cathode of said modulator tube and the control grid of said thermionic relay, a connection between the anode of Vsaid modulator tube and the cathode of said thermionic relay, a resistance and a source of potential connected between the anode and cathode of said modulator tube, a source of modulating potential, a transformer having a primary winding connected to said source of modulating potential and a secondary winding connected between a movable point on said resistance and the control grid of said modulator tube.

2. A device as recited in claim 1, in which a resistance is connected in series with said secondary winding.

3. A device as recited in claim 1, in which a in series with said secondary winding.

yWERNER BUSCHBECK. 

